1. Bituminous Road Deterioration
Christopher R. Bennett
Director - Data Collection Ltd.

2. Base Types and Surface Types and Materials
Asphalt Concrete
Hot Rolled Modified Asphalt
Rubberized Asphalt
Polymer Asphalt Concrete
Soft Bitumen Mix (Cold Mix)
Porous Asphalt
Stone Mastic
Cape Seal
Double Bituminous Surface Dressing
Single Bituminous Surface Dressing
Slurry Seal
Penetration Macadam
Asphalt Mix
Granular Base
Asphalt Base
Asphalt Pavement Base
Stabilized Base
Surface Treatment

3. Pavement Classification System (Bituminous Pavements)

4. Base and Surface Types Over Time

5. Distress Modes Surfacing Distress Cracking Ravelling Potholing
Edge-Break
Deformation Distress
Rutting
Roughness
Pavement Surface Texture Distress
Texture Depth
Skid Resistance
Drainage Distress
Drainage
New
New
New
New

6. Surfacing Distress
Cracking Area: Sum of rectangular areas circumscribing manifest distress (line cracks are assigned a width of 0.5 m), expressed as a percentage of carriageway area.
Structural Cracking
Narrow Cracking (1-3 mm crack width)
Wide Cracking (> 3 mm crack width)
Thermal Transverse Cracking
Ravelling Area: Area of loss of material from wearing surface, expressed as a percentage of carriageway area.

7. Surfacing Distress
Number of Potholes: Number of potholes per kilometer expressed in terms of the number of ‘standard’ sized potholes of area 0.1 m2. A pothole being defined as an open cavity in road surface with at least 150 mm diameter and at least 25 mm depth.
Edge Break Area: Loss of bituminous surface material (and possibly base materials) from the edge of the pavement, expressed in square meters per km. HDM-4 assigns a depth of 100 mm to potholes and edge break area

8. Deformation Distress
Rutting: Permanent traffic-associated deformation within pavement layers which, if channelised into wheelpaths, accumulates over time and becomes manifested as a rut, expressed as the maximum depth under 2 m straightedge placed transversely across a wheelpath.
Roughness: Deviations of surface from true planar surface with characteristic dimensions that affect vehicle dynamics, ride quality, dynamic loads and drainage, expressed in the International Roughness Index, IRI (m/km).

9. Pavement Surface Texture Distress
Texture Depth: Average depth of the surface of a road expressed as the quotient of a given volume of standardized material (sand) and the area of that material spread in a circular patch on the surface being tested.
Skid Resistance: Resistance to skidding expressed by the sideways force coefficient (SDF) at 50 km/h measured using the Sideways Force Coefficient Routine Investigation Machine (SCRIM).

10. Drainage Distress
Drainage: Drainage condition (excellent, good, fair, poor or very poor), which defines the drainage factor.

11. Interaction Mechanisms1
Water
ingress
Further
cracking
Patches
Shear
Uneven
surface
Spalling
Faster
deformation
ROUGHNESS
Potholes
Time
Surface
Lower strength
Area of
Cracking
Rut
depth

12. Roughness Scales BI = 360 IRI^1.12 QI = 13 IRI SI = 5 e^(-0.18 IRI)
International Roughness
Bump Integrator
Quarter-car Index
Present Serviceability
Index
Trailer TRRL
Index
Index
IRI m/km
BI mm/km
QI counts/km
PSI
5.0 1
700 13
4.2
Good Paved 2
1400 26
3.5 3
2200 40
3.0 4
3000 50
2.4 5
3800 65
2.0 6
4700 80
1.7
Good Unpaved 8
6500
100
1.2 10
8300
130
0.6
Poor Paved 12
10000
156 16
14000
210
Poor Unpaved 20
18000
260 24
22000
310
BI = 360 IRI^1.12 QI = 13 IRI SI = 5 e^(-0.18 IRI)
IRI = BI^0.89 IRI = QI / 13 IRI = 5.5 ln (5.0/SI)

13. Paved Road Deterioration Sequence
Input pavement strength, condition, age for initial analysis year
Year Loop
Compute traffic loading
Compute surface distress increment
Compute roughness increment
Scheduled maintenance? Y N
Compute maintenance effects
Condition responsive? Y N
Patching? Y N
Compute post-maintenance condition, strength, age

14. Annual Change in Roughness
Roughness at the End of the Year
Roughness Increment during the analysis year
RIe
RI
Roughness at the Beginning of the Year
Analysis Year
RIa
RIe = RIa + IRI

15. Maintenance Effects IRIb1 = IRIb0 + dIRI + dIRIoper
Roughness at the Beginning of the Year
Roughness at the End of the Year
Roughness Increment during the analysis year
IRIb
dIRI
IRIe
Analysis Year
IRIb
dIRI
IRIe
Analysis Year
dIRIoper
Maintenance Operation Effect
IRIb1 = IRIb0 + dIRI + dIRIoper

16. Annual Change in Roughness

17. Roughness Environmental Coefficient ‘m’ by HDM-4 Climate Zones

18. Pavement Strength
The strength of bituminous pavements is characterised by the adjusted structural number - SNP
The SNP applies a weighting factor, which reduces with increasing depth, to the sub-base and sub-grade contributions so that the pavement strength for deep pavements is not over-predicted. SNPS = SNBASUS + SNSUBAS + SNSUBG SNBASU = contribution from surface and base layers SNSUBA = contribution from sub-base layers SNSUBG = contribution from subgrade S = season

19. Pavement Strength Structural Number (AASHTO)
Contribution of subgrade function of CBR (HDM-III)
Weighting factor, which reduces with increasing depth (HDM-4)

20. SNP Seasonal and Drainage Effects
The average annual SNP used in the models is derived from the dry season SNP, SNPd, and the lengths of the dry SNP = fs* SNPd fs = function of SNPw / SNPd and length of dry season
Drainage effect on pavement strength is modelled through the changes in the drainage factor DF [1 excellent - 5 very poor]
SNPw / SNPd = f = function of DF, rainfall, surface distress

21. SNP Seasonal and Drainage Effects

22. “Final” Structural Number
SNd = *  a * h
SNPd = SNd + sub-base and sub-grade contributions
SNP = fs * SNPd
SNPk = SNP - dSNPK SNPK = “Final” Structural Number SNP = Adjusted Structural Number dSNPK = Reduction in adjusted structural number due to cracking

23. SNP Layer Strength Coefficients

24. Final Structural Number and Benkelman Deflection
if base is not cemented SNPk = 3.2 DEF^ if base is cemented SNPk = 2.2 DEF^-0.63
if base is not cemented
DEF = 6.5 SNPk^-1.6 if base is cemented
DEF = 3.5 SNPk^-1.6
“Final” Structural Number

25. Crack Modelling
Structural Cracking: This is effectively load and age/environment associated cracking.
Transverse Thermal Cracking: This is generally caused by large diurnal temperature changes or in freeze/thaw conditions, and therefore usually occurs in certain climates. For each type of cracking, separate relationships are given for predicting the time to initiation and the rate of progression.

26. Cracking, Ravelling and Potholes Initiation and Progression

27. Crack Initiation ICA=Kcia{CDS2*a0exp[a1SNP+a2(YE4/SN2)] + CRT}
ICA time to cracking initiation, in years
CDS construction defects indicator for bituminous surfacings
SNP structural number of pavement
YE4 annual number of ESALs, in millions/lane
Kcia calibration factor for cracking initiation
CRT cracking retardation time due to maintenance

28. Crack Initiation

29. Crack Progression
CRP retardation of cracking progression due to preventive treatment
Progression of All cracking commences when tA > 0 or ACAa > 0

30. Crack Progression

31. Transverse Thermal Cracking Initiation
ICT = Kcit max[a0, CDS3 (CCT +a a2 HSNEW)]
ICT time to cracking initiation, in years
CCT coefficient of thermal cracking
HSNEW thickness of the most recent surfacing, in mm
Kcit calibration factor

32. Thermal Crack Progression
dNCT incremental change in number of transverse thermal cracks, in no/km
NCTa number of (reflected) transverse thermal cracks at the start of the analysis, in no./km
NCTeq maximum number of thermal cracks, in no./km
Kcpt calibration factor for cracking initiation

33. Ravelling Initiation IRV = Kvi CDS2 a0 RRF exp(a1 YAX)
IRV time to ravelling initiation, in years
YAX annual number of axles, in millions/lane
Kvi calibration factor for ravelling initiation
RRF ravelling retardation factor due to maintenance

34. Ravelling Progression
Progression of ravelling commences when tv > 0 or ARVa > 0
dARV change in area of ravelling during analysis year, % of total carriageway area
SRVa area of ravelling at the start of the analysis year, in per cent
Kvp calibration factor

35. Pothole Initiation
IPT time between the initiation of ACW or ravelling and the initiation of potholes, in years
HS total thickness of bituminous surfacing, in mm
CDB construction defects indicator for the base
YAX annual number of axles , in millions/lane
MMP mean monthly precipitation, in mm/month
Kpi calibration factor for pothole initiation

36. Pothole Progression
dNPTi additional number of potholes per km deriving from distress type i (wide cracking, ravelling, enlargement)
ADISi per cent area of distress i at start of the analysis year
TLF time lapse factor
Kpp calibration factor

37. Edge break dVEB annual loss of edge material, in m3/km
PSH proportion of time using shoulder
AADT annual average daily traffic
ESTEP elevation difference from pavement to shoulder, in mm
MMP mean monthly precipitation, in mm/month
S average traffic speed, in km/h
CW carriageway width, in m
Keb calibration factor

38. Damaged and Undamaged Area
The total road surface will consist of the following:
edge break
potholes
cracking
ravelling
undamaged

39. Rut Depth Modeling
Rutting is defined as the permanent or unrecoverable traffic-associated deformation within pavement layers.
The rut depth model is based on four components of rutting:
Initial densification
Structural deformation
Plastic deformation
Wear from studded tires

40. Rut Depth Progression
Bituminous Roads Deterioration

41. Initial Densification
RDO rutting due to initial densification, mm
YE4 Number of equivalent standard axles
DEF Benkelman beam deflection, in mm
SNP structural number of the pavement
COMP relative compaction, (%)
Krid calibration factor

42. Structural Deformation
Structural deformation without cracking
Structural deformation after cracking

43. Plastic Deformation
RDPD incremental increase in plastic deformation in analysis year, in mm
CDS construction defects indicator for bituminous surfacings
Sh speed of heavy vehicles, in km/h
HS total thickness of bituminous surfacing, mm
Krpd calibration factor

44. Wear by Studded Tires
RDW incremental increase in rut depth due to studded tyres in analysis year, in mm
PASS annual number of vehicle passes with studded tyres in one direction, in thousands
SALT variable for salted or unsalted roads (2 = salted; 1 = unsalted)
Krsw calibration factor

45. Rut Depth Standard Deviation
RDS = a0 RDM
RDS incremental increase in rut depth standard deviation in analysis year, in mm
RDM incremental increase in total rut depth in analysis year, in mm
a0 model coefficient (default =0.5)

46. Texture Depth
TD incremental change in sand patch derived texture depth during analysis year, in mm
TDa texture depth at the beginning of the analysis year
NELV number of equivalent light vehicle passes during analysis year
Ktd calibration factor for texture depth

47. Skid Resistance SFC50 = Ksfc a0 QCV
SFC50 incremental change in side force coefficient during analysis year, measured at 50 km/h
QCV annual incremental increase in the flow of commercial vehicles, in veh/lane/day
Ksfc calibration factor

48. The End